1. Field of the Invention
The present invention relates generally to a wireless communication apparatus and a wireless communication method for detecting electric field intensity of a wireless channel, and a program storing medium.
2. Description of the Related Art
In recent years, for example, a wireless communication system specified in, for example, IEEE 802.15.4 includes a wireless relay device (coordinator) as the center of a network, and a plurality of wireless terminal devices (end devices) existing in the network and performing wireless communication with the wireless relay device.
In such a wireless communication system, wireless communication is performed between the wireless relay device and the wireless terminal devices by using any one of a plurality of wireless channels. To realize stabilized communication environment, the wireless wave interference avoiding technique (for example, frequency agility) of dynamically switching a wireless channel to be used is employed. When using the wireless wave interference avoiding technique, the state of a wireless wave interference of a wireless channel has to be measured by an ED (Energy Detection) scan.
For example, Jpn. Pat. Appln. KOKAI Publication No. 2004-520766 discloses a technique of measuring the qualities of a plurality of wireless channels by a wireless terminal device on a network and collecting the measurement results in a wireless relay device. In such a technique, however, although the wireless wave condition of a wireless channel in the periphery of the wireless terminal device can be grasped, it is difficult to grasp the wireless wave condition of a wireless channel around the wireless relay device. In the wireless communication system, specified in IEEE 802.15.4, a wireless terminal device is usually in a sleep state. At an arbitrary timing when communication becomes necessary, the wireless terminal device wakes up and starts communication. Consequently, the wireless relay device has to remain in a standby state in order to receive data transmitted from a wireless terminal device at an arbitrary timing except when data is transmitted to the wireless terminal device. Therefore, even when a wireless relay device tries to measure a wireless wave condition of a wireless channel around the wireless relay device, it is difficult to distinguish whether the measurement result is an interference wireless wave or a wireless wave used in communication from a wireless terminal device on a network.
Jpn. Pat. Appln. KOKAI Publication No. 2002-158667 discloses a wireless network in which a master station transmits a monitor beacon that prohibits transmission from a slave station for a predetermined time, the slave station which receives the monitor beacon stops packet transmission for the designated period and measures intensity of received electric field during the period, and transmits the measurement result to the master station. According to the technique described in this publication, however, in a system that transmits data from a wireless relay device (master station) to a wireless terminal device (slave station), the wireless relay device forcedly stops data communication with the wireless terminal device to measure the electric field intensity. Consequently, it is not assumed that the technique is applied to a system where data communication starts in response to a request from a wireless terminal device. In the technique descried in the publication, the wireless relay device forcedly stops data communication with the wireless terminal device, so that data transmission/reception to/from the wireless terminal device cannot be performed during the stop period. There is consequently a problem that communication efficiency deteriorates.
Further, to measure the wireless wave interference condition of a wireless channel to avoid wireless wave interference, it is necessary to measure not only a wireless channel currently being used but also a wireless channel to which the wireless channel is switched. To measure a wireless channel to which the wireless channel currently being used is switched, the wireless relay device has to change the wireless channel currently being used to another wireless channel. However, the wireless relay device has to remain in a standby state in order to receive data transmitted from the wireless terminal device. It is difficult for the wireless relay device to change the wireless channel to another wireless channel.
Although there is a technique of providing the wireless relay device with a wireless unit dedicated to measure wireless wave interference, a problem occurs such that the cost increases.